This invention relates generally to fuel filter dehydrator apparatus and more particularly, is directed to a fuel filter dehydrator for use with a ground supply fuel system which automatically shuts off fuel flow upon saturation of the filter dehydrator with water.
The use of water separators or dehydrators for the removal of water from fuel systems is old in the art. Prior art separators and dehydrators are capable of filtering water from the fuel to such a degree that the fuel is acceptable for immediate use. Problems associated with these prior art filtration devices do not ordinarily arise until the device has become saturated with solid particulates, water or ice crystals formed from residual water contained therein. This can result in the discharge of particulates, and/or water into the fuel flow due to the differential pressure in the fuel lines created by the saturation of the filtration device with particulate material and/or water.
In one type of prior art filtration device, the discharge of particulates, water or ice from the filtration device is prevented by placing a sensing device downstream of the filter for mechanically shutting off fuel flow at a predetermined pressure differential across the filtration device.
In another type of filtering device, this valving action is automatically created without further mechanical action by a felt-like mass of water absorptive cellulose which swells to shut off fuel flow as it becomes saturated with water. Exemplary of this type of prior art filtration device is the filter dehydrator disclosed in U.S. Pat. No. 4,242,206 to Estabrooke. In this particular device, a layer of felt-like water absorptive cellulose is provided with a layer of compressed fiberglass wrapped therearound. The fuel flows through the fiberglass and thereafter through the water absorptive cellulose material for filtration and dehydration. The function of the fiberglass material, as stated by Estabrooke, is to emulsify, disperse and deter the release of water droplets within the fuel. However, the dispersing function of the fiberglass layer is inconsistent with the proper operation of the filter as a dehydrator. This is because the felt-like mass of water absorptive cellulose has an inherent porosity which permits small water droplets to pass therethrough. Thus, the emulsifying and dispersing effect of the fiberglass only creates smaller water droplets which are more likely to defeat the filter by passing through the water absorptive cellulose media.